This invention relates to the art of making metal shot and, more particularly, to a method and apparatus for making dry metal shot.
The present invention finds particular utility in connection with making aluminum shot for use, for example, in the steel making industry, and accordingly the invention will be disclosed and described in conjunction with making aluminum shot. At the same time, however, it will be appreciated that the invention is applicable to the production of shot from metals other than aluminum and to the production of shot for uses other than in the steel making industry.
It is of course well known to make metal shot by forming droplets of molten metal and allowing the droplets to descend into a receptacle filled with a coolant such as water to solidify the droplets. Such is shown for example in U.S. Pat. No. 194,271 to Shiver, wherein droplets are formed by vibrating a pan into which the molten metal is poured and the bottom wall of which pan is apertured so that droplets of the molten metal are formed as the metal passes through the apertures. The making of metal shot by such direct liquid cooling is undesirable for a number of reasons including the fact that it is difficult to maintain the cooling fluid at a uniform temperature as is necessary to assure a desired quality with respect to the shot being produced. In this respect, if the cooling liquid is too cool the metal of the shot is adversely affected by the shock of sudden cooling, and if the cooling liquid is too warm the shot tends to adhere to each other, whereby clumps of shot are produced rather than individual pieces of shot. Further, the use of cooling liquid requires having to convey the shot to a dryer, and then having to convey the shot to a point of storage or use. The process therefore becomes very time consuming and expensive. Still further, the liquid cooling and drying can result in the oxidation of the surface of the shot which, while not affecting the shot in use, does affect the appearance thereof. Furthermore, the requirement for conveying the cooled shot from the liquid container to equipment for drying the shot increases both the cost of apparatus and the floor space required to accommodate the equipment.
Apparatus has also been provided to produce shot without the use of a cooling liquid. In this respect, for example, U.S. Pat. No. 3,150,212 discloses the forming of shot by dropping molten metal onto a cooled, rotating drum and then onto an inclined chute from which the shot drops into a receptacle containing an anti-oxidizer. The disadvantage of apparatus of this character is the fact that the rate of production is determined by the axial length of the rotating drum whereby, for a given axial length, production can only be increased by increasing the number of drums onto which the shot can fall. Such cooled, rotating drums are not only expensive to manufacture but also to maintain and, because of the rotating and cooled nature thereof, frequent maintenance is necessary. Still further, regardless of whether a number of single roll units where installed to attain a desired production rate, or a multiple roll arrangement were designed, the cost of the apparatus and the cost of maintaining the same would be undesirably high and the apparatus would require an undesirable amount of floor space.